Current limiter



July 5, 1960 c. J. BussM ErAx. 2,943,904

CURRENT LIMITER Filed March 20 ,l 1959 2 sheets-sheet 1 QIUUUUI INVENTOR ATTORNEY July 5, 1960 c. J. BussoM ETAL 2,943,904

CURRENT LIMITER Filed March 20, 1959 l 2 Sheets-Sheet 2 ATTORNEY CURRENTLIMITER Charles J. Bussom, Fairmount City, and Donald L. Say,Brookville, Pa., assignors to Sylvania Electric Products Inc., acorporation of Delaware Filed Mar. 20, 1959, Ser. No. 800,734

7 Claims. (Cl. 31'6-27) This invention relates to electron tubemanufacturing and in particular to the aging of electron tubes.

It is common practice in the art, after the parts of a tube have beenassembled and sealed within an air exhausted envelope, to transfer thetubes to an aging rack, usually in the form of a conveyor having barswith tube sockets thereon and wherein the tubes inserted in the socketsare heated by application of abnormally high voltages to the iilamentaryheater and other electrodes within the tube. The eiect of this heatingis to raise the temperature of the parts within the tube to higher thantemperatures they would be subjected to in normal use, and, bycontrolling the heating, permanent changes are effected in thegeometrical conguration in the electrodes within the tube. In theparticular case of the second or screen grid, if the grid be elliptical,rectangular or. of other'shape displaying major and minor diameterswiththe minor diameter perpendicular to the active face of the cathode, theheating of the tube causes a permanent increase in the minor diameter ofthe grid, with a permanent increase of spacing between the screen gridand control grid. This increase in spacing reduces the anode currentthat would otherwise iiow through the tube and correspondingly changesother characteristics of the tube, such as trans-conductance and screengrid current. The reduction in current flow is desirable, sincethetubes, prior to aging, have widely diierent characteristics; but, byaging the tubes, the top level of anode current in all of them arereduced to a lower level, thereby reducing the spread above anarbitrarily designated lower level of current. Thus tubes with moreuniform characteristics than prior to aging, are produced.

However, the prior art methods and machines lowered the current levelsof all tubes alike, including those` wherein current levels wereinitially too low, thereby failing to obtain tubes with as good uniformcharacteristics as could be obtained by means of the present invention.

It is an object of this invention to provide a system whereby, while alltubes are subjected to treatment which may bring about a lowering of thecurrent level in the tube, the treatment is varied as required for eachtube to bring about a fairly uniform characteristic of current iloWthrough all of the tubes.

It is amore specific object of the invention to bring about an expansionof the screen grid of a tube, when required, tosuch a degree as to lowerthe cathode current to a predetermined value. l

VAnother object of the invention is to provide a system whereby althougha group of tubes is'treatedi'for lower-v` ing the cathode currenttherein, the treatment of each tube Yis, individually controlled tobringabout a substantially.. equal cathode current in each of the tubes.

Other-objectspjof the invention will become apparent uponV.consideration of the followingspecication, when takenjn conjunctionlwith the accompanying drawings inwhich: Y :.4 i.

, Fig... l Yis a diagrammatic vertical view of the aging rack PatentedJuly 5, 1960 employed in the invention, with a conveyor about the rack.

Fig. 2 is a fragmental plan view of one of the bars used on theconveyor.

Fig. 3 is a fragmentary portion of the underface of the bar.

Fig. 4 is an end View of the bar.

Fig. 5 is a wiring diagram of the circuitry involved in the inventionand Fig. 6 is a view of a type of tube which into the sockets on thebars.

Referring tothe drawings in greater detail, in Fig. l there isdiagrammatically illustrated a conveyor frame 10, around whichtravels aconveyor 11 of two spaced parallel chains 1,2 (only one chain beingshown) running in the direction of the arrow and havingV a verticalascending side 13, an upper horizontal run V14, a -vertical descendingside 16 and a lower horizontal run 18. 'Ihese chains are drivenintermittently, for example one step every twenty five seconds, by aGeneva drive 20 whose drive shaft 22 may be variably driven, as througha Reeves transmission, not shown, to vary the timing of intermittentmovement ofthe conveyor.V Spanning the chains are bars 24, each providedwith a number of tube receiving sockets 26. To simplify the description,but not as limitative of the invention, specific numbers of parts and aspecific type oftube will be referred to although it will be obviousthat other vnumbers of parts and other types of tubes may be selected.For an example,l each bar, of which there may be one hundred andfourteen, is provided with nine sockets 26, each adapted forcee-ive atube, as tube 28, eachV socket being provided with seven contacts 30 tocorrespond with the pins 32 on the tube. Each of the ascending anddescending sides of the conveyor may accommodate nineteen of the barsand the lower and horizontal runs may each accommodate thirty eightbars. The sockets are loaded with tubes to be aged at the loadingstation at the right of Fig. 1 at about the third indexed position ofthe bar from the bottom run, and the tubes are removed at the unloadingstation on the descending run of the conveyor at about the third bar maybe plugged above the bottom run. As a result, in this instance, the

contacts in a row as there are sockets on the bar multiplied by thenumber of contacts in each socket; since seven contacts have beenselected for each of nine sockets,

there will be sixty three fixed contacts `in a row. The

socket contacts are brought to the lower faces of theLA bars 24 whereinprinted circuitry 40, similar for each socket, leads the contacts to arow of shoes 42 mounted on the bar to correspond with the lateralspacing of the fixed spring contacts. The nine wires leading to corre,-sponding shoesV on each socket, as for example, the anode k connectedshoes, are connected into a bundle 44, each bundle leading to theterminals of a polarized plug 46. 'Ihe plugs from one bar all lead to aplug-in panel 50.' Each panel has seven plug sockets 52 to respectivelyreceive the pins lof the plugs. Each of the contacts of the plug-insockets is fed with individually regulated current. at suitablevoltages, so that each contact of the sockets on the bars can be fedwith any desired voltage at any desired indexed position of the bars.This allows Vfor extreme exibility in aging of the tubes. In accordancewith applicants invention, at one offth'e" indexed positions of thebars, for-example at the titty? sixth indexed position removed from theloading position," the wires from the spring contacts are differentlybundled# .upon the current ow.viathe, screen:grid.andthe-poten- Hereftheseven wires originating Vfrom a Vsocket are made into a group, as group58, and the nine groups of wires 58 from the nine sockets are fed to arelay box 60 Within which .are nineprelays 62, seeFig. 5, and associatedequip Vment, as will be described. Each relay comprises. an: 5

electromagnetic coilz64; a pairg offfixedlback contacts .166, 68, a pairof lixed front contacts 7 0, 72, andantarmaturef; carryinga pair:of tiedtogether movable; arms :76 and 78, the arm 76 alternatively contactingcontacts 66 and .76; and the arm 78 alternatively, contacting contacts`63 10 A wire 80 connects movable arm 76Lw-ith Ythe springcontact 381leading to. they anodecf4 atube. A'4 wire- 82 ,connects movable arm 78with-a spring contact 38fleading to the V#t l'iorf'co'ntrolgrid ofthesame tub'ei A wire 84 Y connects :ft2Y grid-lori?` screen spring`VContact Eliand re;

lay contact 66`A`wie 86 connects cathode Vspringl contact- 38` andrelayA contact 72. The'heater'wires 87, 88 lead from springcontacts 38VV to a variablevtransformer 90 soI as to feed'any`desired-volt'age-to` the heater, and a suppressor grid springfcontactconnectedv wire 92V leadsto one-side of a Vclosed switch 94Whicli'switch is. connected atv its-,other side to the cathode lead 86.The contact 68V isegroundedwhile the contact 70 is open circuited; 25

VY The contact 66Y in addition to being connected to line84.isvconnected via a load` lamp` 96 to asou1'ce'98l o-f`D;C. potentialwhichjmay be varied, at will. 'Ihel contactY 772isfconnect'edryiaaleadrV 100 to the'movable arm101"of lafpotentiometer4102, grounded atoneend, 30

Aand connectedfat` its. other'uend to the cathode of" a self biased-grid'controlled gas iilled" tube 104, asfal type' 2D21, whose ,grid` isground via a resistor 10.6. By

Y K' varying the positionV oflthe potentiometer`- arm 101, the' Y'voltage required 'to tireY theV tube 104 may bevaried at l35 will,Current tothe relay. coil. 64 is fed from a D C.

source,V cutV olf with each indexrmovement of the bars,.

' as byea'microswitch 107 opened `with every index of the Y bars, via acurrent limiting resistor l108 and the anodekof-the gas filled tube,when the tube isred. The state 40 of tube 104 may'V be indicated by ahigh resistance indi-` cating lampV as'a neon lamp 110 inrsh'unt withthe-tubev l104'and its potentiometer-.102.. g

Each; of the nine tubes on Vthe bar atl thek titty-sixthV index"position registers With an ,individualY electrode 45 switchingcircuit,exactlynlike the one `described andil- Iustratedin Fig.` 5.V IfVcathodecurrent of a tube under testis; suticientlyV high,to maintainvover 2.0{-volt's.bias.

(in the casev oli the ZDZl type tube) over theYV lower part ofpotentiometer 1.02.,V the tuble 104 willfnot fre.50

Y andthe .circuit remainsas-show'n in the said igure. In.

this,` position, the, screen Vgrid Yoffthe tube .28'. under` test Yis"conductingvrcurrentwhile .the anode is not. Also the control grid.Vis ,shortedY to` thecathode. current ow'th'rough the screen gridis highand the- 55 grid' lateralsY ofjthelscreen -grid become. suiciently. hot

Therefore, Y. the

tolexpandbeyondtheir elasticlimits. As the Vgridvvires expand, theymove' farther from the controlrgrid,.wherer tiometer 102 diminishes.When-low enough, thefnegav60 tive -bias Yon, thegrid. oflthe-gas filled.tube decreases-V and thetubelires andA conducts untilthe. next index off lefbar.V Piringgof' the.tube..10.4-fwill. causecurrent to ow.throughgthe relay Acoil 64. thereby throwing the?,

'movable arm` 76 and ..7 8 .against the back,xedcontacts566'165V and.6.8 andthe` current ,iovvV throughthe tube yZllcisrdi-V-l rectedviathega'node and. scrveen: grid-ntiedrtogethervas one unit.VAlso`t-he.controhgrid.ofv theatubeZt'iscon-1 nected. to, the ground,`imposing a. negativebias on0 the" `tentiometer 102, therebylimitingranodefcurrent through thee/tube.'4 This controll'edf andlowerivaluefcurrent is y' permanent deformation offthe grid twin"@eene-'75 Vvthe sockets, s aid relay mechanism comprisinga coisponsive'to the magnitude of said current 'floweand'ropv `If a tubeinitially, with the circuitn theposiionshoyvll..

results desired. Also the current detecting means need 'Y notnecessarily-be. af,-gas'.lledi tube sinceicontact making meters andother than gas filled; grid controlled tubes 5 can be used as Well, astriodes with' A.C. supply to the anode.

Nor need the detecting mechanism be confined to Ythecathode. circuitsince it could be placedin any tube'circuitrwhere current flowvarrieswith electrode deformation.. Y. l a What is'claimed as newfis: f

l. In a machine for aging electrontubesyhaving .a;g

,Y cathode, control. grid, screen grid; and anode, V.thefcom-Lrk-binatidn. comprising aconveyorV frame, ang indexiblel conveyorV on theframe, bars carriedrby'the conyeyor;^ andk tube socketsl for said tubeson each gbar, contacts on each bar. Wiredto individual contacts, inthetube:

sockets, contacts mounted on the'conveyorV frame, one;V .for eachcontactzon the bars at each ofv ajinultilgzlicity5.`

of positions .ofV the barsgsaid` frame mountedA contacts! Y Vbeingconnectedindividually to individual sources; off-1 voltage, .thecontactsonthe frame. atone positionopi the bars, leading: to relay.v mechanism,switchingUllsarlsn formingyparti-of said mechanism; for normally; estabflishing aicurrent'owfromescreen; grid to cathode;withinfY tubesV in thesockets, said relay'mechanism havingaafcirf cuit element throughwhichtubecurrentflows; and responsive tofthe magnitudezof'said currenttogswitchgthe'.TV

currentso,-thatiit..lows viathe anodeand screen grid 1 Vtothecathodefoftthentfube.r Y l 2. -In a machine for aging electron tubeshaving;` aff cathode, controlv grid, screen grid andV anode; theecomfA YbinationV comprising a Vconveyor frame, an .indexible- Y conveyor `onsaid frame, bars carriedybythe conveyori.

and tube socketsy -for said tujbeson eachY bar, contactso'n:l

each .barwired to individualcontacts in the: tube sockets`contacts-.mounted` on the conveyorframe, onefforfeaclifv contact on .thebars at each' of a'multiplicityr-of vpositions?.` Y Y'of-.the bars,said:Y frame mounted: contacts: b`eingf.c0uf.

nected individually to individual. sources of voltagefthe: contactsorrthetramef at` one positionfof the barsV lead ing.A torelayfcmechanism, switching Vmeans `forming-part Y of said.: mechanisme'for.; normally; establishingI a 1 current'- owfrom screen` gridto.cathode: WithinA tubes` ine-.thef sockets,v saidrelay :mechanismcomprising a-:coil respon-z4 Y sive tothe magnitude ofi said: currentzflow-fand operative upon-fan armature having'fcontacts, saidcontactsinonev position of thevarmature connecting? the; 'screenV gri'd to@ i anvidleY contact andl'in; anotherv positionnof theI karmatureconnectingsthescreenjgridfto Vthe anode:

3. In a machine for aging-electron1 tubesj-havingfa. f cathode;control'grid, screen g'ridr andeanodefthe com` bination comprising aconveyorr frame; A,an \5ind'exib le confveyor oni said-1 framev `barscarried byfthectmveyer'j.-.and,`V tube sockets for said tubes on .each\barcontactsi.onw each 'bar-vr Wired to Yindividual .contacts in theftubsockets, contactsmountedon the` conveyor.frarne.one forfeachV contac t.on..the `'bars at ,eachV of. a-multiplicity voiigpo'sitions-'of,thefbarsfsaid fr-ame;mounted-contacts--being connected L.individually ,to individual souresgo voltage?, Y bars". leading to.rrelay. mechanism. switching. means; forming' part of. said mechanismvfor normals-establish'. rent ovv'r'fr'om screen grid'to' cathodejwithin' tubes rative upon an armature having two contacts, one of saidcontacts in a rst position of the armature connecting the screen grid toan idle contact and in a second position of the armature connecting thescreen grid to the anode, the other of said contacts in said rstposition connecting the control grid to the cathode and in said secondposition connecting the control Igrid to a negative voltage with respectto the cathode.

4. In a machine for aging electron tubes having a cathode, control grid,screen grid and anode, the combination comprising a conveyor lframe, anindexible conveyor on said frame, bars carried by the conveyor and tubesockets for said tubes on each bar, contacts on each -bar wired toindividual contacts in thertube sockets, contacts mounted on theconveyor frame, one for each contact on the bars at each of amultiplicity of positions of the bars, said frame mounted contacts beingconnected individually to individual sources of voltage, the contacts onthe frame at one position of the bars leading to relay mechanism,switching means forming part of said mechanism for normally establishingVa current flow from screen grid to cathode within tubes in the sockets,said relay mechanism comprising a coil in series with a self biasinggrid controlled tube having a resistor in its grid circuit, an armaturecontrolled by the coil, a contact movable with the armature in a firstposition to tie together the screen grid of the tube being aged and itsassociated anode and in a second position to disconnect the two, asecond contact movable with the armature which in said rst positionconnects the control grid of the tube being aged directly with itsassociated cathode and in the second position interposes at least aportion of the resistor into the said direct connection.

5. In a machine for aging electron tubes having a cathode, control grid,screen grid and anode, the combination comprising a conveyor frame, anindexible conveyor on said frame, bars carried by the conveyor and tubesockets for said tubes on each bar, contacts on each bar wired toindividual contacts in the tube sockets, contacts mounted on theconveyor frame, one for each contact on the bars at each of amultiplicity of positions of the bars, said frame mounted contacts beingconnected individually to individual sources of voltage, the contacts onthe frame at one position of the bars leading to relay mechanism, a coiland switching means forming part of said relay mechanism for normallyestablishing a current ow from screen gridA to catho'de Within. tubes inthe sockets, said relay mechanism including a'source of D.C. voltage, arelay having a rst, idle, front contact and a second front contactconnected to the cathode of the tube, a third, back contact connected tothe source o'f D.C. voltage and to the screen grid, a fourth,backcontact connected to ground and an armature having two poles a firstone of which is movable between the first and third contacts and thesecond one of which is movable between the second and fourth contacts,said rst pole being connected to the anode and the second pole to thecontrol grid, a grid controlled gas filled tube in series with the coil,means to break the current o'w through the gas filled tube, said gaslled tube having a resistance in series with the cathode and ground andbiasedly connected at a non cathode connected portion of the resistancewith its control grid, and a connection between the resistanceintermediate of its length and the second front contact.

6. In a machine for aging electron t-ubes having a cathode, controlgrid, screen grid and anode, the combination comprising a conveyorframe, an index'ible conveyor on said frame, bars carried by theconveyor and tube sockets for said tubes on each bar, contacts on eachbar wired to individual contacts in the tube sockets, contacts mountedon the conveyor frame, one for each contact on the bars at each of amultiplicity of positions of the bars, said frame mounted contacts beingconnected individually to individual sources of voltage, the contacts onthe frame at one position of the bars leading to relay mechanism,switching means forming part of said'mechanism for normally establishinga current ow from screen grid to cathode within tubes in the sockets,said relay mechanism comprising a coil responsive to the magnitude ofsaid current iow and operative upon an armature having contacts, saidcontacts in one position of the armature connecting the screen grid toan idle contact and in another position of tue armature connecting thescreen grid to the ano'de, said screen grid, in both positions of thearmature, being connected to a source of potential.v Y

7. A system for controllably agingelectron tubes having a cathode, acontrol grid, a screen grid and an anode,

said system including a source of D.C. voltage, a relay having a coil, atirst, idle, front contact and a second, front contact connected to thecathode of the tube, a third, back contact connected to the source ofD.C. voltage and to the vscreen grid, a fourth, back contact connectedto ground and an armature having two poles a first one of which ismovable between the first and third contacts and the second one of whichis movable between the second and fourth contacts, said first pole beingconnected to the anode and the second pole to the control grid, a gridcontrolled gas lled tube in series with the coil, means to break thecurrent ow through the gas lled tube, said gas filled tube having aresistance in series with the cathode and ground and biasedly connectedat a non cathode connected portion'of the resistance with its controlgrid, and a' connection between the resistance intermediate of itslength and the second, front contact.

Y References Cited in the iile of this patent UNITED STATES PATENTSFlowers Aug. 27, 1957

